LATERAL BRACING FORCES IN COLUMNS WITH 2 UNEQUAL SPANS

Elastic columns with two spans of arbitrary length ratio are investiga ted. The base is pinned and may include a rotational spring. An elasti c support acts between the spans, and the top is pinned or supported e lastically. An axial load is applied. For perfect columns, the effects of the internal support location and the spring stiffnesses on the cr itical load and buckling mode are determined. Under special conditions , an ideal spring stiffness exists, such that the elastic supports do not deflect when the column buckles. Imperfect columns with an initial deflection of the same shape as the buckling mode of the correspondin g perfect column are also considered. Deflections and bracing forces a t the elastic supports are obtained as functions of the axial load, an d approximations in terms of the amplification factor are discussed. T hese results are utilized in a sequel to this paper, which examines de sign rules for the required stiffness and strength of bracing.